1. Field of the Invention
The present invention relates to a method for measuring a fine pattern, an apparatus for measuring a fine pattern, and a record medium that can store therein a program to measure a fine pattern and can be read by using a computer. More particularly, the present invention relates to an exposing technique in a process for manufacturing a semiconductor device. Moreover, the present invention relates to a method for separate an optical proximity correction pattern from a fine pattern such as a reticle pattern and the like.
2. Description of the Related Art
An exposing technique (lithography technique), which is a basic technique of a micro fabrication used in a process for manufacturing a semiconductor integrated circuit, is a technique for optically transcribing a pattern of a photo mask, such as a reticle and the like, based on a circuit pattern onto a film deposited on a wafer surface. Etching, film deposition, impurity injection or the like is carried out in accordance with the pattern transcribed onto the wafer. The semiconductor integrated circuit is manufactured by the repetition of those operations.
Associated with a hyperfine structure of a pattern dimension of a semiconductor device, an optical proximity effect induced when the reticle pattern is transcribed onto the wafer has large influence on the electrical properties of the semiconductor device.
Actually, as shown in a sketch before a correction on a left column of FIG. 1A, a transcription of a rectangular reticle pattern onto the wafer causes a so called pattern end shortening to be induced, in which a corner portion of the transcription pattern is not transcribed and it is rounded. Also, a transcription of a line pattern as shown in a sketch before a correction on a left column of FIG. 1B results in a dimensional variation (rough and fine dependency) caused by environmental change in a pattern periphery, as the word goes, in which a central portion of a line at a center is thinly transcribed. The optical proximity effect causes the semiconductor device to be largely deviated from a design pattern, which makes a predetermined operation of the semiconductor device difficult.
As a method to-solve this problem, an OPC technique is used for giving an correction pattern (OPC pattern) to a portion to which the pattern is not transcribed because of the optical proximity effect of the reticle pattern. Actually, as shown in a sketch after a correction on a right column of FIG. 1A, when the reticle pattern is rectangular, if a correction pattern is given around contour of four corners in the reticle pattern, only the roundness of the corner in the transcription pattern is suppressed, and the shortening of the pattern end is suppressed. Also, as shown in a sketch after a correction on a right column of FIG. 1B, a correction pattern is given to a portion adjacent to a line pattern, in order to make a line width in the periphery wider, which avoids the line to be made locally thinner.
By the way, in the conventional process for manufacturing a semiconductor, there may be a case that a pattern is directly observed on a wafer transcribed by using a reticle in which the optical proximity effect is corrected. However, there is no case that a reticle pattern is not directly observed in which the optical proximity effect is corrected. In short, whether or not the correction pattern is accurately given to the reticle is not checked on the reticle, and it is checked by using the pattern which is transcribed from the reticle onto the wafer. Thus, the correction pattern on the reticle is not evaluated.
Also, when the pattern on the reticle is evaluated, there is not a definite algorithm for discriminating between a non-correction pattern and a correction pattern.
The present invention is proposed to solve the above-mentioned problems in the conventional technique. It is therefore an object of the present invention to provide a method for measuring a fine pattern and an apparatus for measuring a fine pattern which can effectively measure a large number of optical proximity effect correction patterns by using a simple method, and a record medium that can store therein a program for measuring a fine pattern and can be read by a computer.
Another object of the present invention is to provide a method for measuring a fine pattern and an apparatus for measuring a fine pattern which can develop a mask process having a high quality, and a record medium that can store therein a program for measuring a fine pattern and can be read by a computer.
In order to attain the above-mentioned objects, the first feature of the present invention lies in a method for measuring a fine pattern, which at least comprises the steps of a first step of capturing an image of a fine pattern; a second step of extracting a contour of the fine pattern from the image of the fine pattern; a third step of capturing a standard figure of the fine pattern; a fourth step of superimposing the standard figure on the contour by enlarging or reducing the standard figure while maintaining an aspect ratio thereof; a fifth step of extracting an intersection of the contour and the standard figure; a sixth step of extracting a differential region surrounded with the contour of the fine pattern, the standard figure and the intersection; a seventh step of extracting a correction pattern region from the differential region; and an eighth step of measuring the correction pattern region. Here, the standard figure of the fine pattern corresponds to a non-corrected fine pattern. It may be prepared from a design pattern before a correction of a design pattern, such as a CAD data and the like, or it may be freely prepared by a engineer. Also, it can be extracted from the contour of the fine pattern.
According to the first feature of the present invention, since the correction pattern region can be measured by using a simple method, it is possible to effectively inspect a reticle in which the optical proximity effect is corrected. The standard figure is superimposed on the contour of the fine pattern by enlarging or reducing the standard figure while maintaining an aspect ratio thereof. Also, its size is changed in response to the contour of the fine pattern. Thus, a stable measurement can be done independently of a magnification of the image of the fine pattern and the like.
So, when a lithography process is developed, a measurement data of the correction for optical proximity effect pattern of the reticle can be effectively obtained in large quantities. Thus, it is possible to carry out the correction for optical proximity effect of the reticle much effectively. Also, when a mask process is developed, it is possible to check whether or not the correction pattern is desirably generated. Hence, it is possible to develop the mask process with a high quality. On the other hand, conventionally, the correction pattern can not be measured even in an actual mask management. So, there is only one method to test a success or failure of a mask once the pattern is formed on the wafer. However, it is possible to detect a error of the reticle before the pattern is actually formed on the wafer.
In the first feature of the present invention, the seventh step may be a step of extracting all the differential regions extracted at the sixth step, as the correction pattern region. Also, the seventh step may be composed of: a process for measuring an area of the differential region extracted at the sixth step; and a process for extracting the differential region having an area equal to or wider than a predetermined threshold as the correction pattern region. Moreover, the seventh step may be composed of: a process for indicating the differential region in a polar coordinate; a process for preparing a weighting function having a weight in an existence range of a correction pattern; a process for multiplying the differential region indicated by the polar coordinate by the weighting function; and a process for extracting as the correction pattern region the differential region after it is multiplied by the weighting function.
Also, in the method for measuring a fine pattern according to the first feature of the present invention, it is desirable that between the sixth step and the seventh step, there are further a step of comparing the number of differential regions with the number of correction patterns added to the standard figure and a step of measuring the area of the differential region. And, it is also desirable that the seventh step is divided into first to third cases as described below. At first, in the first case that the number of differential regions is equal to the number of correction patterns, the seventh step is a step at which all the differential regions are extracted as the correction pattern region. In the second case that the number of differential regions is greater than the number of correction patterns and two blocks are generated at a predetermined interval in a distribution of the areas of the differential regions, the seventh step is a step at which the differential region having the area equal to or wider than a predetermined threshold is extracted as the correction pattern region. And, in the third case that the number of differential regions is greater than the number of correction patterns and two blocks are not generated at a predetermined interval in a dispersion situation of the areas of the differential regions, the seventh step is composed of a process for indicating the differential region by using the polar coordinate, a process for preparing a weighting function having a weight in an existence range of a correction pattern, and a process for multiplying the differential region indicated by using the polar coordinate by the weighting function, and a process for extracting as a correction pattern region from the differential region after it is multiplied by the weighting function.
Here, it is desirable that the process for preparing the weighting function is composed of: an operation for determining a difference between a design pattern after a correction and a standard figure, and extracting a correction pattern; an operation for extracting a center of gravity in the standard figure; an operation for indicating the correction pattern in a polar coordinate with the center of gravity in the standard figure as an original point; and an operation for using the correction pattern indicated by the polar coordinate, and preparing a weighting function in which an existence range of the correction pattern is assumed to be 1 and a non-existence range of the correction pattern is assumed to be 0. It is also desirable that the standard figure in this case is prepared from a design pattern before the correction. Also, the process for preparing the weighting function may be composed of: an operation for indicating a contour of the fine pattern in a polar coordinate with the center of gravity in the standard figure superimposed at the fourth step as an original point; an operation for carrying out a frequency analysis, and removing a high frequency component of the contour indicated by the polar coordinate; an operation for carrying out a frequency analysis, and extracting an existence range of an correction pattern from a low frequency component of the contour indicated by the polar coordinate; and an operation for preparing a weighting function in which an existence range of the correction pattern is assumed to be 1 and a non-existence range of the correction pattern is assumed to be 0.
Also, it is desirable that the fourth step is composed of a process for indicating the contour in a polar coordinate; a process for indicating the standard figure in a polar coordinate; a process for preparing a weighting function having a weight in a non-existence range of an correction pattern; a process for multiplying the contour of the fine pattern by the weighting function; a process for multiplying the standard figure by the weighting function; a process for approximating the standard figure to the contour; and a process for indicating the contour of the fine pattern and the standard figure in an orthogonal coordinate.
Here, it is desirable that the process for preparing the weighting function having the weight in the non-existence range of the correction pattern is composed of: an operation for determining a difference between a design pattern after the correction and a standard figure, and extracting the correction pattern; an operation for extracting a center of gravity in the standard figure; an operation for indicating the correction pattern in a polar coordinate with the center of gravity in the standard figure as an original point; and an operation for using the correction pattern indicated by the polar coordinate, and preparing a weighting function in which an existence range of the correction pattern is assumed to be 0 and a non-existence range of the correction pattern is assumed to be 1. By the way, it is desirable that the standard figure in this case is prepared by a design pattern before the correction. Also, the process for preparing the weighting function having the weight in the non-existence range of the correction pattern may be composed of: an operation for indicating a contour of the fine pattern in a polar coordinate; an operation for carrying out a frequency analysis, and removing a high frequency component of the contour indicated by the polar coordinate; an operation for carrying out a frequency analysis, and extracting as an existence range of an correction pattern from a low frequency component of the contour indicated by the polar coordinate; and an operation for preparing a weighting function in which an existence range of the correction pattern is assumed to be 0 and a non-existence range of the correction pattern is assumed to be 1.
Moreover, it is desirable that the fourth step of superimposing the standard figure on the contour by enlarging or reducing the standard figure while maintaining an aspect ratio thereof, when the fine pattern is a pattern which is not a closed region, is composed of: a process for extracting a middle point between any two points in a portion corresponding to a non-corrected portion, on left and right contours extracted from the fine pattern; and a process for generating two parallel lines positioned at a distance equal to half of a line width from the middle point, as the standard figure.
The second feature of the present invention lies in an apparatus for measuring a fine pattern, comprising: a photographing device for obtaining an image of a fine pattern; a memory for storing therein a pattern data of a standard figure of the fine pattern; and an image processor which at least have a function of extracting a contour of the fine pattern from the image of the fine pattern, a function of superimposing the standard figure of the fine pattern on the contour of the fine pattern, a function of extracting an intersection of the standard figure and the contour of the fine pattern, a function of extracting a differential region surrounded with the standard figure, the contour and the intersection of them, a function of extracting a correction pattern from the differential region and a function of measuring the correction pattern.
The third feature of the present invention lies in a record medium, which can be read by a computer that stores therein a program for measuring a fine pattern and which comprises: a first step of capturing an image of a fine pattern; a second step of extracting a contour of the fine pattern from the image of the fine pattern; a third step of capturing a standard figure of the fine pattern; a fourth step of superimposing the standard figure on the contour by enlarging or reducing the standard figure while maintaining an aspect ratio thereof; a fifth step of extracting an intersection of the contour of the fine pattern and the standard figure; a sixth step of extracting a differential region surrounded with the contour of the fine pattern, the standard figure and the intersection; a seventh step of extracting a correction pattern region from the differential region; and an eighth step of measuring the correction pattern region.